Machine to Machine (M2M) communication is a development trend of intelligent communication in future, and a 3rd-generation (3G) mobile communication system and its Long Term Evolution (LTE) system need to support a Machine Type Communications (MTC) function. An MTC device (MTC User Equipment (UE)) may have parts of the various M2M communication features, e.g., low mobility, small volume of data to be transmitted, being insensitive to communication delay, and extremely low power consumption requirement. In an existing M2M network based on a Global System for Mobile (GSM) technology, an operator finds that, when the MTC UE operates in some scenarios, e.g., a basement, a shopping mall or a corner of a building, significant signal attenuation may occur because a radio signal is shielded seriously, and it is impossible for the MTC UE to communicate with the network. An in-depth coverage for the network in these scenarios may remarkably result in an increase in the network building cost, including cost for the newly-added equipment, cost for network planning, and cost for manual maintenance. Along with the development of the radio communication technology, an M2M service will be deployed in the LTE network, so the operator hopes that the network coverage may be effectively increased in the subsequent LTE-based radio communication technology, so as to improve the coverage for the MTC UE in the above-mentioned scenarios and for the other UEs in similar scenarios.
In order to improve the coverage for the UEs and meet the operator's demand, one possible way is to introduce a continuous transmission mechanism over a physical channel, so as to improve the coverage through a combination gain of repeated transmission. This mechanism is subsequently referred to as repetition mechanism.
For the UE which supports a coverage enhancement mechanism (i.e., the repetition mechanism), once a coverage enhancement function is enabled, it means that the data may be continuously retransmitted over some physical channels. At this time, when timing maintenance related to the physical channels is still performed in accordance with a method specified in an existing standard, the UE may not operate normally (the so-called “timing maintenance” mainly refers to the determination of a timing window or a start time point for a timer, the determination of an effective time point for any other timing information, and the like). The so-called timing maintenance related to the physical channel refers to that a start time point and an effective time point for the timing maintenance are related to the transmission over the physical channel.
Taking a random contention access procedure for an LTE-Advanced (LTE-A) system as an example, an existing random access procedure will be described hereinafter.
The UE selects a random access Preamble and a Physical Random Access Channel (PRACH) resource, and transmits a message 1 (Msg1) carrying the selected random access Preamble to a base station using the PRACH resource.
A Random Access Response Window (RAR window) is then started by the UE 3 ms after the transmission of the Msg1. A typical value for the RAR window is 10 ms.
The base station receives the random access Preamble, calculates an uplink (UL) Timing Advance (TA), and transmits to the UE an Msg2 over a Downlink Shared Channel (DL-SCH), e.g., a Physical Downlink Shared Channel (PDSCH). The Msg2 is a Random Access Response (RAR) and at least contains UL TA information and UL grant information for an Msg3.
The UE then waits in the RAR window for the reception of the RAR. When no RAR has been received, the UE may determine that the random access is failed.
Then, the UE transmits the Msg3 over an Uplink Shared Channel (UL-SCH), e.g., a Physical Uplink Shared Channel (PUSCH), so as to schedule the uplink transmission for the first time. The Msg3 carries identification information of the UE.
The UE enables a Media Access Control (MAC)-Contention Resolution Timer after the Msg3 has been transmitted, receives an Msg4 during the operation of the timer, determines whether or not the contention is successful in accordance with the identification information of the UE carried in the Msg3 as well as the Msg4, and stops the timer when the contention is successful. The Msg4 is transmitted over the DL-SCH.
For the UE under the coverage enhancement mechanism, the Msg1 is transmitted, e.g., 25 times. In accordance with the existing standard, the RAR window is started after the transmission of the Msg1 for the first time, so no RAR may be received in the RAR window. As a result, a random access failure occurs for the UE, and the system cannot operate normally.